Assuming there are 4 of you then you'll be taking a taxi to/from the city centre ( If you weren't planning to do this you should change your plans to use a taxi - 4 bus fares would not be far off the cost of a taxi and it's much faster given the Guinness Storehouse is quite a step from where the buses will drop you )

What I would do is then leave the bags at the hotel .. I can't imagine they wouldn't do this for you ( or ask them can you have a 2pm late checkout on one of the rooms ) ... Then on the way back simply get the taxi driver to go via the Premier Inn and wait outside while you get the bags .. it would be a max 5 minute detour on the way back to the airport to do this.

Simplest option ... it will only cost you a few minutes extra on the way back and you'll save loads of time and potential refusal with trying for an early check in of your luggage ( I don't know what the timetable is on the day you're going but as noted there's often a large gap in the middle of the day with check in closing around 10.30 and not opening again until your flight - so probably around 13.00 )